Control system for fluid fuel burners



Nov. 4, 1941. w. L. M GRATH 2,261,536

CONTROL SYSTEM FOR FLUID FUEL BURNERS Filed April 18, 1940 331mm William. 14. Mi Gnu-1'1 A)" MM Patented Nov. 4, 1941 bONTROL SYSTEM FOR. FLUID FUEL BURNERS William L. McGrath, Philadelphia, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application April 18, 1940, Serial No. 330,345

17 Claims.

This invention is directed broadly to control systems for fluid fuel burners, such as the usual oil burner, and more specifically to systems which are relatively simple and inexpensive and include a minimum number of parts.

One of the principal objects of the. invention is to provide a control system in which a timer or power device is energized in response to a demand for heat for energizing the fuel burner for a predetermined period of time and then deenergizing it again, and in which a device responsive directly to combustion acts mechanically to prevent the deenergization of said fuel burner if combustion is established within said predetermined period.

A further object is to obtain intermittent ignition by connecting the combustion responsive device to an ignition switch so as to open it in the presence of combustion.

A still further object is to provide a mechanical interlock for preventing the power device from initiating operation of the fuel feeding device unless the combustion responsive device is in its cold position at which time the ignition switch is closed.

Reference is made to my copending application Serial No. 280,302 filed June 21, 1939, which covers a control system of the same general type as the one disclosed in the present application, but which has constant ignition.

This invention will be more clearly understood when the following specification is read in the light of the accompanying drawing, in which Figure l is a diagrammatic showing of my control system; and

Figures 2, 3, 4, and are detail views showing certain parts of the system in various positions of operation.

Referring now to Figure l of the drawing the reference numeral ll indicates a space thermostat including a bimetallic coil 12 and a switch arm l3.- The bimetallic coil is so arranged thaton a decrease in temperature it causes the switch arm l3 to engage the stationary contact 14. A timer or power device indicated generally at [5 comprises a bimetallic blade 16 connected at its upper end to the bracket I1. This timer is adapted to be heated by means of the electric heating element I8. The lower end of the blade 16 carries a pin 19 which may if desired be rotatably mounted with respect to the blade 16. Blade I6 is adapted to warp in a direction to move its lower end toward the left as seen in Figure 1 upon energization of the heater mostat is indicated at 22.

4 is connected to rod 24 by means of a slip friction connection 26. Stops 21 and 28 limit the rotation of the lever 25 and the slip friction connection 26 permits over travel of the rod 24 in response to further temperature variation at the thermostat 22. It will therefore be seen that due to the slip friction connection and the stops 21 and 28 the lever 25 will be rotated in response to changes in temperature at the thermostat 22 rather than in response to any predetermined degree of temperature. The result is that the lever 25 rotates in a counter-clockwise direction in response to the establishment'oi combustion and in a clockwise direction upon the extinguishment of the flame. v

A switch lever 30 is loosely pivotally connected to the lever 25 as shown at 3|. The upper end of this lever is provided with two arms 32 and 33 with which the pin 19 is adapted to cooperate. Normally the arm 32 rests by gravity against the pin 19. The upper end of the lever 30 is therefore positioned by means of the bimetal i6 and the lower end of the lever 36 is positioned by means of the combustion responsive lever 25'. A

} motor control switch 35 in the form of a curved glass tube is mounted at an intermediate point on the lever 30. A pair of electrodes 36 and 31 extend into the tube at its midpoint so that when the tube is in a horizontal or nearly horizontal position the mercury 38 will bridge the two electrodes but when it is tipped. either one way or the other the electrodes will be unbridged.

A mercury ignition switch 40 is connected to the lower end of a levef 4| which is in turn pivotally su'spendedfrom the fixed pin 42. Electrodes 43 and 44 extend into one end of the mercury switch tube 46 and are adapted to be bridged by means of the mercury 45. An arm 46 on the lever 25 is adapted to engage a projection 41 on the lever 41 to hold the mercury switch 40 in closed position as long as the lever 25 is abutting the stop 21 indicating the absence of combustion in the furnace. When the lever 25 is rotated in response to combustion the arm 46 releases the lever 4| and gravity is permitted to rotate the lever in a direction to open the circuit through the switch 46. n

The upper portion of the lever 41 is provided circumstances is adapted to latch against projection on the lever 30 to prevent the bimetal l5 from moving the upper end of the lever 30.

This control system is provided with the usual burner motor 52 and ignition device 53 for lgniting the fuel delivered by the motor 52. The electrical power for operating the above system is supplied by the line wires 54 and 55.

Operation Assume that the temperature in the space to be controlled is above the control point and that the switch |3|4 is therefore open. Assume also that this condition has obtained for a sufficient length of time for the bimetal IE to assume its cold position as indicated in Figure 1. Assume also that the absence of combustion in the combustion chamber of the furnace has caused the thermostat 22 to rotate the lever 25 against the stop 21. Under these conditions the electrodes 36 and 31 of the motor control switch 35 will be unbridged and the electrodes 43 and 44 of the ignition switch 40 will be bridged. Inasmuch as the switch is in series with both the burner motor 52 and the ignition device 53 they will both be deenergized.

On a decrease in space temperature the switch arm |3 will be brought into engagement with -the stationary contact |4 completing a circuit from line wire 55, conductor 51, bimetal l2, switch arm l3, contact l4, conductor 58, electric heater I8, conductor 59, switch 50, and conductor 6|, back to the other line wire 54. The closure of this circuit will energize the heater i8 which will raise the temperature of the bimetal l6 and establish the following circuit: from line wire 55 through a conductor 63, electrode 31, electrode 36, conductors 64 and 65, electrodes 44 and 43, conductor 66, ignition device 53, and conductor 61 back to the line wire 54. This circuit ener gizes the ignition device 53. The burner motor 52 is connected in parallel with the ignition switch 40 and ignition device 53 by means of the conductors 58 and 83. Therefore the closure of the switch 35 simultaneously energizes the burner motor 52, and ignition 53. The position of the bimetal I6 and the two switch operating levers 30 and 4| is shown in Figure 2 under these conditions. It will be understood that as the mercury switch tube 35 is curved the electrodes 36 and 31 will be bridged for a definite time interval as the lever 3|! is slowly rotated by bimetal I6.

Let it be assumed that combustion does not take place. will be no change in temperature in the thermostat 22 and therefore no movement of the lever 25. As the bimetal l6 continues to heat it will continue rotating the lever 30 in a counterclockwise direction until this lever passes over center with respect to the pin 3| upon which it is freely pivoted, at which time it will drop until the arm 33 engages the pin IS on the bimetal |6 as shown in Figure 3. At this time the switch 35 will be open thereby deenergizing the burner motor 52 and the ignition device 53. The parts will remain in this position as long as thespace thermostat H is calling for heat until manual intervention takes place. In order to reset the device for a restart it is necessary first to open the switch 60 until the bimetal I has Under these circumstances there i had an opportunity to return to its cold position. Due to the spacing between the arms 33 and 32 this movement cannot move lever 30 to reclose the switch 35. In order to accomplish this it is necessary to push in the reset button 12 and manually rotate the lever 30 to the position which it occupies in Figure 1. The switch 60 may then be reclosed and the system is in a condition to make another attempt at a normal start.

If the switch |3|4 is still closed by the bimetal |2 the bimetal |6 will again be heated and the parts will return to the position shown in Figure 2 at which time the burner motor and ignition device are energized. If combustion is established the thermostat 22 will be heated and will rotate the lever 25 in a counter-clockwise direction. The thermostat 22 and bimetal I6 must be so related that the lever 25 will keep in step with the lever 3|! and maintain the control switch 35 in closed position. When the lever 25 has been rotated against the stop 28 and the bimetal l6 has warped to its full extent the parts will assume the positions shown in Figure 4 at which time the switch 35 will be closed thereby maintaining the burner motor 52 energized. It will be noted that as the lever 25 rotates counter-clockwise it releases the lever 4| and permits it to swing in a clockwise direction by gravity to open the ignition switch 40 thereby deenergizing the ignition device 53 as shown in Figure 4. This is the running condition of the system. 1

In the event that the space thermostat ll becomes satisfled the bimetal l2 separates the switch arm H from the contact H and deenergizes the electric heater l3. This permits the bimetal l6 to cool and warp toward the right thereby permitting the lever 30 to rotate in a clockwise direction and open the switch 35. Opening of switch 35 deenergizes the burner motor so that the flame within the combustion chamber is extinguished, and the thermostat 22 will then cause lever 25 to rotate in a clockwise direction. It will be noted in Figure 5 that when the bimetal I6 has returned to its cold position that the projection 5| on the lever 30 latches over the projection 50 on the lever 4| so that if the heater I8 should be energized at this time the bimetal l6 would be mechanically held and hence incapable of warping to the left and rotating the lever 30. This prevents the switch 35 from being closed and energizing the burner motor 52 unless the ignition switch 40 has been closed by the lever 25. When the lever 25 returns to its cold position against the stop 21 the arm 46 engages projection 41 on the lever 4| and rotates this lever in a counter-clockwise direction thereby closing the ignition switch 40 and removing the projection 5|! from the projection 5| freeing the lever 38 for movement by the bimetal |6. The parts at this time have returned to the positions shown in Figure 1.

If the system should be in running condition as shown in Figure 4 and a flame failure should occur then the thermostat 22 would immediately rotate the lever 25 against the stop 21 and the lever 30 would consequently be rotated by the lever 25 in a counter-clockwise direction and would pass over center with respect to the pin 3| and drop into the position shown in Figure 3 thereby opening the switch 35. As in the case of original ignition failure the lever 30 would remain in this position until manual intervention.

It will therefore be seen that I have designed a relatively simple and inexpensive control system which uses a single timer or power device and a single switch for controlling the burner motor and ignition switch. It will also be seen that the systemcomprising the above parts operates safely in the event of an initial ignition failure or a subsequent flame failure.

Various changes and modifications of the above invention will doubtless occur to those who are skilled in the art and I therefore desire that it be understood that I intend to be limited only by the scope of the appended claims and not by the specific embodiment of the invention disclosed.

I claim as my invention:

1. A control system comprising in combina tion, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for a predetermined period of time and then reopening said switch as said timer moves in response to a demand for heat, and means movable in timed relation to said timer in response to the establishment of combustion for preventing said timer from reopening said switch as long as there is a demand for heat, the movement of said timer being unaffected by said last mentioned means.

2. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for a predetermined period of time and then reopening said switch as said timer moves in response to a demand for heat, and means movable in timed relation to said timer in response to the establishment of combustion for preventing said timer from reopening said switch as long as there is a demand for heat, the movement of said timer being unaffected by said last mentioned means, and means preventing the reclosure of said switch, except upon manual intervention, once it has been opened by said timer during a demand for heat.

3. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for a predetermined period of time and then reopening said switch as said timer moves vent said timer from reopening said switch while there is a demand for heat.

4. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for a predetermined period of time and then reopening said switch as said timer'moves in response to a demand for heat, means mechanically associated with said control switch, a thermal element responsive to the heat of combustion, mechanical connections between said I last mentionedmeans and said thermal element, said thermal element acting in response to the establishment of combustion to keep said means in step-with said timer to prevent said timer from reopening said switch while there is a demand for heat, and means preventing the reclosure of said switch, except upon manual intervention, once it has been opened by said timer during a demand for heat.

5. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for 'a predetermined period of time and then reopening said switch as said timer moves in response to a demand for heat, means movable in timed relation to said timer in response to the establishment of combustion for preventing said timer from reopening said switchas long as there is a demand for heat, an ignition device for igniting the fuel fed by said fuel feeding device, and an ignition switch in control of said ignition device, said combustion responsive means closing said switch in cold position and opening said switch in r esponse to the'establishment of combustion.

6. A control system comprisin in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for a predetermined period of time and then reopening said switch as said timer moves in response to a demand for heat, means movable in timed relation to said timer in response to the establishment of combustion for preventing said timer from reopening said switch as long as there is a demand for heat, an ignition device for igniting the fuel fed by said fuel feeding device, an ignition switch in control of said ignition device, said combustion responsive means closing said switch in cold position and opening said switch in response to the establishment of combustion, and means preventing said timer from closing the control switch for the fuel feeding device unless the combustion responsive means is in its cold position.

7. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves in one direction in response to a demand for heat and in the opposite direction when there is no demand for heat, said timer first closing said control switch for a predetermined period of time and then reopening said switch as said timer moves in response to a demand for heat, means movable in timed relation to said timer in response to the establishment of combustion for preventing said timer from reopening said switch as long as there is a demand for heat, an ignition device for igniting the fuel fed by said fuel feeding device, an ignition switch in control of said ignition device,"'said combustion responsive means closing saidswitch in cold position and opening said switch in response to the establishment of combustion, and a latch for mechanically preventing said timer from closing the control switch for the fuel feeding device in response to a demand for heat, said combustion responsive means releasing said latch when it closes the control switch for the ignition device.

8. In a control system of the class described, an electrical fuel feeding device, a control switch therefor, a lever adapted to actuate said switch, a timer, said timer, upon energization in response to a demand for heat, moving said lever to close said switch for a predetermined period of time and then open it again, and means acting in response to the establishment of combustion for moving said lever in a direction to maintain said switch closed if it has not already been opened by said timer.

9. In a control system of the class described, an electrical fuel feeding device, a control switch therefor, a lever adapted to actuate said switch, a timer, said timer, upon energization in response to a demand for heat, moving said lever to close said switch for a predetermined period of time and then open it again, means acting in response to the establishment of combustion for moving said lever in a direction to maintain said switch closed if it has not already been opened by said timer, and means preventing the reclosure of said switch by said lever, except upon manual intervention, once it has been opened by said timer during a demand for heat.

10. In a control system of the class described, an electrical fuel feeding device, a controlswitch therefor, a lever adapted to actuate said switch, a timer, said timer, upon energization in response to a demand for heat, moving said lever to close said switch for a predetermined period of time and then open it again, means acting in response to the establishment of combustion for moving said lever in a direction to maintain said switch closed if it has not already been opened by said timer, an ignition device for igniting the fuel fed by said fuel feeding device, and an ignition switch in control of said ignition device, said combustion responsive means maintaining said ignition switch closed when cold and opening said switch in response to combustion.

11. In a control system of the class described, an electrical fuel feeding device, a control switch therefor, a lever adapted to actuate said switch, a timer, said timer, upon energization in response to a demand for heat, moving said lever to close said switch for a predetermined period of time and then open it again, means acting in response to the establishment of combustion for moving said lever in a direction to maintain said switch closed if it has not already been opened by said timer, an ignition device for igniting the fuel fed by said fuel feeding device, an ignition switch in control of said ignition device, said combustion responsive means maintaining said ignition switch closed when cold and opening said switch in response to combustion, and a latch engaging said lever to prevent said timer from closing said control switch on a demand for heat, said combustion responsive means releasing said latch when it is in cold position.

12. In a control system of the class described, a floating lever, a mercury switch carried by said lever, said mercury switch comprising an elongated tube and electrodes extending into said tube at a mid point, mercury within said tube, combustion producing means including an electric fuel feeding device, a circuit therefor including said electrodes, a timer operatively associated with said lever at one point, combustion responsive means operatively associated with said lever at a second point, and means energizing said timer in response to a demand for heat to cause said timer to rotate said lever in a direction to cause the mercury to bridge said electrodes, further rotation of said lever causin said mercury to unbridge said electrodes again after a predetermined length of time, said combustion responsive means acting to move said lever in a manner to prevent the timer from rotating it far enough to unbridge the electrodes again, providing combustion occurs first.

13. In a control system of the class described, a floating lever, a mercury switch carried by said lever, said mercury switch comprising an elongated tube and electrodes extending into said tube at a mid point, mercury within said tube, combustion producing means including an electric fuel feeding device, a circuittherefor including said electrodes, a timer operatively associated with said lever at one point, combustion responsive means operatively associated with said lever at a second point, and means energizing said timer in response to a demand for heat to cause said timer to rotate said lever in a direction to cause the mercury to bridge said electrodes, further rotation of said lever causing said mercury to unbridge said electrodes again after a predetermined length of time, said combustion responsive means acting to move said lever in a manner to prevent the timer from rotating it far enough to unbridge the electrodes again, providing combustion occurs first, said switch requiring manual intervention to return it to its original position once it has been opened by the timer on a failure of combustion.

14. A fuel burner control system comprising an electrical fuel feeding device, a power device which when energized renders said fuel feeding device operative to deliver fuel to a point of combustion for a predetermined period of time and then renders said fuel feeding device inoperative again, means for energizing said power device, an ignition device for igniting the fuel, combustion responsive means preventing said power device from rendering said fuel feeding device inoperative if combustion is established during said predetermined period of time, means deenergizing said ignition device after combustion is established, and means mechanically preventing said power device upon energization from rendering said fuel feeding device operative unless said ignition deenergizing means has returned to a position where it is operative to energize said ignition device.

15. A fuel burner control system comprising an electrical fuel feeding device, a power device which when energized renders said fuel feeding device operative to deliver fuel to a point of combustion for a predetermined period of time and then renders said fuel feeding device inoperative again, means for energizing said power device, an ignition device for igniting the fuel, an ignition switch, combustion responsive means preventing said power device from rendering said fuel device inoperative if combustion is established during said predetermined period of time, said combustion responsive means opening said ignition switch upon the establishment of combustion, and means controlled by said combustion responsive means preventing said power device upon energization from rendering said fuel feeding device operative unless said ignition switch is closed.

16. A control system comprising in combination, an electrical fuel feeding device, a power device which slowly moves from a first to a second ,device also opening said ignition switch, and

means preventing the energization of said power device unless said ignition switch is in closed position.

17. A control system comprising in combination, an electrical fuel feeding device, a power device which slowly moves from a first to a second position upon energization and slowly returns to said first position upon deenergization,

means for energizing said power device to first render said fuel'feeding device operative for a predetermined period of time and then render it inoperative again as it moves into said second position, an ignition device, an ignition switch in control thereof, a combustion responsive device for preventing said power device from rendering said fuel feeding device inoperative as it movesinto said second position in the event that combustion has been established, said combustion responsive device also opening said ignition switch, and latch means controlled by said combustion responsive device for preventing movement of said power device upon energization thereof unless said combustion responsive device is in cold position at which time it has .closed said ignition switch.

WILLIAM L. McGRATH. 

